Thin sheets of certain types of uniaxial magnetic material are capable of supporting single wall magnetic domains magnetized in a direction opposite to that of the adjacent region. Furthermore, the single wall domains, or bubbles, can, under proper conditions, be generated, propagated, annihilated and sensed.
One particular method of propagating these bubbles, called the field-access method, utilizes a rotating in-plane magnetic field. This field, cooperating with a patterned layer of soft magnetic material, preferably overlying the material supporting the bubbles, will cause the bubbles to propagate along a path defined by the pattern and in synchronism with the rotating magnetic field. This characteristic, plus the interaction of bubbles with each other has led to the development of devices for performing logic operations with the bubbles. More particularly, these devices rely upon the mutual repulsion between adjacent bubbles to signal, by the selective movement of one bubble, the presence of an adjacent bubble. Logic functions are performed in a binary fashion, for example, by assigning the binary value 1 or 0 to the presence or absence of a bubble respectively. Since the bubbles move synchronously, the absence of a bubble, called a void can also be said to move synchronously. Thus a serial stream of bubbles and voids may represent data which can be considered binary. With two such streams, logical functions may be performed with an output stream representing the logical combination of the input streams. One form of bubble AND circuit is shown in Danylchuk et al, U.S. Pat. No. 3,651,496. Another illustration of an AND/OR gate and an EXCLUSIVE OR gate can be found in an article by Sandfort et al, entitled "Logic Functions for Magnetic Bubble Devices," appearing in IEEE Transactions on Magnetics, pages 358 through 360 (September 1971). Of course, as illustrated in each of the foregoing references, each distinct logic function requires a different overlay pattern. While this differentiation is not fatal to the utility of these devices, it is inflexible and tends to increase design cost. It is desirable to achieve an universal logic device. That is, a device which is capable of performing one of many, or all, possible logic functions. The desirable universal logic device could be personalized, in the final manufacturing stages, to perform one of the many logic functions it was capable of. By postponing the personalizing step to the interconnection phase of manufacturing, the device has even more desirable characteristics in that the manufacture of all logic devices would be identical. Further postponement is possible if dynamically alterable logic can be implemented as will be described herein.
Personalizable logic devices, with the foregoing characteristics, have also been discussed in the semi-conductor field. In particular Henle et al, in an article entitled "Structure Logic," appearing in the 1969 Fall Joint Computer Conference Proc. (pp. 61-68), discussed read-only storage which is just a systematic personalizable logic array. Fleisher et al, in an article entitled "The Writeable Personalized Chip," appearing in the June 1970 issue of Computer Design, at pages 59 through 66 explore the logical requirements for a semiconductor universal logic device.
A bubble logic device which is minimally personalizable is illustrated in Morrow et al, U.S. Pat. No. 3,543,255. In particular, see FIG. 31 and column 6, related thereto. Morrow et al disclose a three-input device comprising input channels A, B and C. The device is capable of producing streams of bubbles on output channels A, B and C wherein the data on each output channel is identical to the data on the input channel or, a single output channel with the output equal to A.B.C (where . represents AND). This device is minimally personalizable since the device is capable of either producing a logical AND between all of its inputs or performing no logic function at all. It is apparent that the Morrow et al disclosure is quite removed from the desire for a logic array capable of performing a wide variety of logical functions.
The foregoing statement applies, with even greater force, to the specific logical circuits including the AND, AND/OR and EXCLUSIVE OR gates previously referred to. Finally, the Fleisher et al article, while dealing with the logical requirements for a semiconductor logic array, provides little, if any, insight into the specific requirements for logical bubble devices. Dynamic personalization is difficult with semiconductor devices because of the volatility of control information upon power cutoff. Bubble based devices, in contrast, do not lose personality as long as the bias field remains. A "Magnetic Logic Arrangement" disclosed in U.S. Pat. No. 3,541,522, describes a universal logic cell which are controlled by multiple conductor lines and perform different logic functions in response to different control pulses. The cells are basically two-input cells. A multiplicity of these cells could be considered a logic array. However, the many conductor lines are not amenable to LSI manufacture, nor are the conglomeration of two input cells amenable to high-level logic functions nor pipelined operation. The first bubble logic device which is amenable to array logic is described in a copending patent application Ser. No. 351,665 filed 4/16/73) now published application B 351,665 published on Jan. 28, 1975 under the Trial Voluntary Protest Program. The device is based on the counting of bubbles to execute logic in symmetrical switching functions, while the present invention is based on the logic arrangement of more conventional logic connective components. In contrast to the application Ser. No. 351,665, the present invention needs no clear operation after each logic operation, and its personalization data are in parallel rather than in series, hence it lends itself more readily to pipelined operation.